A fluid ejection module, for example, as employed in an ink jet printer, typically includes a fluid path from a fluid supply to a fluid nozzle assembly that includes nozzles from which fluid (ink) drops are ejected. Fluid drop ejection can be controlled by pressurizing fluid in the fluid path with a pumping actuator, for example, a piezoelectric deflector. Although many configurations are possible, a typical fluid ejector or printhead module has a line or an array of fluid ejector units with a corresponding array nozzles, ink paths, and associated actuators, and drop ejection from each nozzle can be independently controlled. The printhead module and the medium can be moving relative one another during a printing operation. In a so-called “drop-on-demand” printhead module, each actuator is fired to selectively eject a drop at a specific location on a medium.
In one example, a fluid ejection module can include a semiconductor printhead body and a piezoelectric pumping actuator. The printhead body can be made of silicon etched to define pumping chambers. Nozzles can be defined by a separate substrate (i.e., a nozzle layer) that is attached to the printhead body. The piezoelectric actuator can have a layer of piezoelectric material that changes geometry, or flexes, in response to an applied voltage. Flexing of the piezoelectric layer causes a membrane to flex, where the membrane forms a wall of the pumping chamber. Flexing the membrane thereby pressurizes ink in a pumping chamber located along the ink path and ejects an ink drop from a nozzle at a nozzle velocity. Aspects of the construction and operation of fluid ejection modules known to the art can be found, for example, in U.S. Patent Pub. No. 2005/0099467, entitled “Print Head with Thin Membrane” filed by Bibl et al on Oct. 8, 2004 and published May 12, 2005, the entire contents of which is hereby incorporated by reference. U.S. Patent Pub. No. 2005/0099467 describes examples of printhead modules and fabrication techniques.